The present invention relates to metal production, particularly steel. More precisely it relates to metallurgical vessels such as refining converters with bottoms provided with permeable refractory elements.
Metallurgical processes are known in which a molten metal bath is subjected to pneumatic stirring or bubbling by controlled injection of a stirring fluid, usually an inert gas such as nitrogen or argon, through permeable refractory elements incorporated in the usual refractory lining of the vessel which contains the bath. The injected inert gas emerges under the surface of the bath contained in the vessel. The abovementioned permeable refractory elements for blowing the inert gas are in general provided in the bottom of the vessel, as disclosed for example in the French Pat. No. 2,322,202 or U.S. Pat. No. 3,259,484. The steel-making process which includes this stirring technique and blowing of refining oxygen through the top of the vessel is used at the present time throughout the world and known under the commercial name "LBE process" (Lance-Brassage-Equilibre). This process tends to provide, as its name indicates, a balance between metal and slag, so as to accumulate to a large extent the respective advantages of the conventional top oxygen blowing and bottom oxygen blowing refining processes.
Numerous solutions have been proposed for providing in the refractory elements sufficient selective permeability so as to produce a satisfactory flow of stirring fluid and at the same time avoid penetration of the molten metal in the reverse direction. One of these solutions is described in the published European patent application No. 21,861 and consists in forming passage zones of very small size in a usual compact refractory material. This is obtained either by incorporating longitudinal (in blowing direction) foreign bodies within a monolithic refractory mass, or by juxtaposing refractory plates with interposition of calibrated distance pieces therebetween. These elements like any refractory material inevitably wear out as a result of their contact with the molten metal. This wear is accelerated because of the gas blast which causes substantial convection movements at the level of the blowing elements and whose induced effects are felt also on the service life of the surrounding conventional refractory. At the present time it is however possible with the elements of the above mentioned type to limit the rate of wear thereof substantially to the wear of the conventional refractory lining which forms the bottom, so as to have a service life comparable with the service life in the conventional top oxygen blowing converters of LD type. Another problem which arises in practice is that the permeability of the blowing elements tends to diminish during use. This phenomenon seems somewhat paradoxical, since it accompanies the normal progressive wear of the bottom and therefore it might be thought that because the elements wear out at practically the same rate as the bottom, their permeability should to the contrary increase with time, following a reduction of the pressure losses in the blowing spaces. However in practice the permeability of the blowing elements substantially diminishes during use, and unless they are frequently replaced their permeability no longer allows the desired gas flow to pass therethrough. This is not only highly disadvantageous, but also takes away all advantages obtained by a service life of the elements equal to the service life of the bottom.